Dimensions.—Diameter of the disk 0.2 to 0.25; length of the radial spines 0.005 to 0.018, basal breadth 0.001 to 0.003.
Habitat.—Pacific, central area, Stations 266 to 268, surface; fossil in Barbados and Sicily.
3. Stylotrochus helianthus, n. sp.
Spongy framework of the whole disk irregular. Thirty to fifty very large, conical radial spines, about as long as the diameter of the disk, and at the base two to four times as broad as one mesh of the framework (without internal prolongations).
Dimensions.—Diameter of the disk 0.15 to 0.2; length of the radial spines 0.16 to 0.24, basal breadth 0.008 to 0.016.
Habitat.—Pacific, central area, Station 272, surface.
4. Stylotrochus rhabdostylus, Haeckel.
Spongy framework of the whole disk irregular. Four very large marginal primary spines crossed in two equatorial diameters, perpendicular one to another, and between them numerous (twelve to twenty or more) smaller secondary spines. The latter arise from the margin, whilst the former pierce the disk and are nearly united in its centre. All the spines are cylindrical, the smaller as broad as one mesh, the larger three to six times as broad.
Dimensions.—Diameter of the disk 0.2; length of the four main spines 0.15 to 0.3, breadth 0.01 to 0.02; length of the accessory spines 0.05 to 0.1, breadth 0.005.
Habitat.—Fossil in the rocks of Barbados.
5. Stylotrochus heteracanthus, Haeckel.
Spongy framework of the whole disk irregular. Ten very long needle-shaped marginal spines (symmetrically distributed), and between them numerous very fine, shorter, accessory, bristle-shaped spines.
Dimensions.—Diameter of the disk 0.16; length of the main spines 0.16, basal breadth 0.002; length of the secondary spines 0.03.
Habitat.—Mediterranean (Messina), surface.
Subgenus 2. Stylospongia, Haeckel, 1862, Monogr. d. Radiol., p. 473.
Definition.—Spongy framework of the disk in the inner part with concentric rings or spiral convolutions, in the outer part quite irregular.
